Coffee's Dirty Little Secret

A riddle for summer: if coffee is best served cold when it’s hot out, why boil and brew what needs to be iced?

Cold-brewing, or Toddy brewing, is the answer. Todd “Toddy” Simpson claims to have tasted cold-brewed coffee while traveling in Peru in 1964, and to have brought the “ancient Peruvian process” back to the U.S. But the truth is far less mysterious.

The truth is, if you put something in water—and that something is at all water soluble, meaning it can dissolve—it will infuse the water with its flavor. Age whiskey in a sherry cask and it takes on flavor from the wood. Put berries or herbs in your vodka for a few months, and you’ve got infused vodka. Coffee works the same way. Put coffee grounds in water for twelve hours, and boom! You’ve got coffee. (In fact, essentially that’s all cold-brewing is.) Obviously, heat accelerates the process, but that’s not all it does. Heat also makes coffee far more acidic, which some coffee tasters demand for top “cup quality.” Jim Reynolds, brewer emeritus and longtime taster for Peet’s Coffee & Tea, says he’s always considered the flavor of cold-brewed coffee to border on insipid and bland (though he admits to using it in cocktails in the '70s). But the tides of taste may be turning against him. Important coffee shops—from Stumptown Coffee out of Portland, to Gimme! Coffee in NYC—are going cold. Cold-brewing, once relegated mainly to the home, is catching on in cafés across the country, and here’s why:

“With temperature change comes change in taste, but because cold-brewed coffee eliminates most of that temperature change, flavor is locked in. In other words, your day-old cold-brew won’t taste stale like day-old coffee.”

1. Same vim, less vinegar: different chemistry, lower acid. Remember that first time you drank coffee, as a kid, and the taste didn’t quite live up to that amazing smell? Cold-brewing does a lot to close the smell-taste gap. Taste is in the chemistry, and exposing coffee grounds to hot water releases oils that won’t dissolve at lower temperatures. These oils are full of acidic compounds that give coffee its famous bitter bite. But along with that bite comes acid-shock, which anesthetizes the tongue and prevents the taster from perceiving the subtle nuances in coffee’s flavor. Sure, that acid may be nice in a hot cup of coffee, but for iced coffee, it’s a detriment; it doesn’t let you perceive coffee’s luscious fruitiness. Is it any wonder that so many people add so much milk and sugar?

According to a study done by Toddy, cold-brewed coffee is 67 percent less acidic than hot-brewed. Without all that acid, the burnt flavor that plagues hot-brewed coffee is eliminated. Plus, the reduced acid makes it healthier for your stomach and your teeth.

2. Less acid means more flavor: Prepare to taste what you’re drinking. Cold-brewed iced coffee has big advantages, like, for example, it tastes better. Since cold-brewing produces a low-acid drink, coffee’s other flavors are more readily detected. Those undertones of chocolate, fruit, and nuts jump to the forefront. Matt Lounsbury, director of operations at Stumptown, explained that the coffee shop has just started offering cold-brewed this year because “it’s just a really nice, smooth cup of iced coffee.” Asked about his favorite beans for cold-brewing, he said, “The single origins tend to do really well with cold brew, particularly the Latin American and South American coffees.” Mike White, regional manager for Gimme!, agrees that cold-brewing “produces a much more balanced flavor with increased sweetness.” For cold-brewing he suggests beans “from the Bufcafe COOP in the Butare region of Rwanda. We've also had great success with bourbon and caturra from the Asobagri COOP in HueHuetenango, Guatemala,” he said. “It's important to change it up though; I discover new favorites all the time.” And for good reason: With cold-brewing allowing so many more coffee flavors to shine through, your bean of preference is likely to change regularly.

Additionally, the flavor of cold-brewed coffee won’t change over time. Cold-brewed coffee has never been hot, so its chemistry doesn’t change as it cools. As soon as you filter out the grounds, you’ve got a stable solution. With temperature change comes change in taste, but because cold-brewed coffee eliminates most of that temperature change, flavor is locked in. In other words, your day-old cold-brew won’t taste stale like day-old coffee.

3. Cold-brewing is easier than pie. Don’t be intimidated by a new process; cold-brewing coffee couldn’t be easier. All you need is pitcher or a jar with a lid—a mason jar works perfectly—and something to strain out the grounds. Combine one cup of coarsely ground beans with four cups of cold or room temperature water, give the mixture a stir, and let the magic of infusion go to work. The mixture should sit for about 12 hours, so make a batch at night and it will be ready to drink in the morning. Before drinking it, though, strain the solution through a coffee filter, a fine mesh sieve, or layered cheesecloth so you don’t get a mouth full of grounds. Filter the mixture once or twice, and you’ve got yourself delicious coffee that will stay good for about 10 days. A French press can also be used: Mix the grounds and water in that, then use the press mechanism as the filter as you would with hot coffee.

If you’re a technophile, cold-brewing machines do exist, but all they’re providing is agitation to mix up the solution, and an easy way to strain and store the coffee. You can be fancy without a machine. All you need to do is shake up the steeping grounds a few hours in. This is more than sufficient to mix the steeping cold-brew so it’s reasonably homogenous. The lazy truth about colloidal suspensions, like coffee or tea (where tiny particles are suspended in a water-based solution), is that dispersive forces do all the mixing for you. There are going to be equal concentrations of flavor throughout.

4. Avoid the Starbucks siren’s caffeine call and save your money for better beans. Cold-brewing exposes expensive coffee for what it is: a ripoff. Expensive coffee makers? Unnecessary. Using vinegar to break up the calcium carbonate deposits in your coffee maker? What coffee maker? The only thing that matters is the beans.

5. The truth will set you free: cold-brewing beyond iced coffee. Another wonder of cold-brewing is the versatility of the product. Because you’re dealing with a more stable solution, you can do almost anything with it. If you like your coffee hot, add boiling water to the more concentrated syrup; you’ll have fresh hot coffee with the taste and low-acid benefits of cold-brewing. If you find that perfect strength cold-brewed mix, but don’t want ice diluting it, freeze the mixture and use coffee ice-cubes. As they melt, the iced-coffee won’t get any weaker. It’s perfect for a picnic or a day on the beach. (But be careful. Ice cubes often pick up taste from the other things in your freezer.) Many recipes don’t call for brewed coffee, because it’s just too acidic, but cold-brewed coffee is perfect for adding the coffee flavor, without the acid. It’s great for baking or marinating, and it’s perfect for a nice cool coffee cocktail.

How long will it be before the giants like Starbucks and Peet’s follow suit? Even Peet’s Reynolds admits that if it becomes a big enough trend they may give it a try.